Fix regressions with regards to route-set creation on early dialogs.

Fix regressions with regards to route-set creation on early dialogs.

This fixes two main issues:

1. Asterisk would send a CANCEL to the route created by the provisional response
   instead of using the same destination it did in the initial INVITE.
2. If a new route set arrives in a 200 OK than was in the 1XX response (perfectly
   possible if our outbound INVITE gets forked), then the route set in the 200 OK
   needs to overwrite the route set in the 1XX response.

(closes issue ASTERISK-19358)
Reported by: Karsten Wemheuer
Tested by: Karsten Wemheuer
patches:
   ASTERISK-19358.patch uploaded by Mark Michelson (license 5049)
   ASTERISK-19358.patch uploaded by Stefan Schmidt (license 6034)

Review: https://reviewboard.asterisk.org/r/1749
........

Merged revisions 355732 from http://svn.asterisk.org/svn/asterisk/branches/1.8

git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/10@355733 65c4cc65-6c06-0410-ace0-fbb531ad65f3